Electrochemical trepanning process and apparatus to accomplish the same



K. F. TRAGER May 14, 1968 ELECTROCHEMICAL TREPANNING PROCESS AND APPARAT TO ACCOMPLISH THE SAME 3 Sheets-Sheet 1 Filed March 13, 1967 INVENTOR AfMPfS/I Tenet-A BY W A. 60M,

ATTORNEY 3,383,296 TUS 5 Sheets-Sheet 2 May 14, 1968 K. F. TRAGER ELECTROCHEMICAL THEPANNING PROCESS AND APPARA TO ACCOMPLISH THE SAME Filed March 13, 1967 mm M 4mm a G W? 2 H F /F G 8 a P r m P 2 a% J W? V O \\\N w -39 N. w 2 G 00% m a ATTORNEY May 14, 1968 K. F. TRAGER ELECTROCHEMICAL TREPANNING PROCESS AND APPARATUS TO ACCOMPLISH THE SAME Filed March 13, 1967 3 Sheets-Sheet 3 INNXNDAKNMWNV WANG l ll lil m mv L 4 INVENTOR Kim/ f: 7794625? ATTORNEY United States Patent 0 3,383,296 ELECTROCHEMICAL TREPANNING PROCESS AND APPARATUS T0 ACCOMPLISH THE SAME 8 Claims. (Cl. 204-143) ABSTRACT OF THE DISCLOSURE An electrochemical machining apparatus having a recessed dielectric back-up member to hold the metal slug eroded by a hollow electrode tool.

This application is a continuation-in-part of application Ser. No. 563,232, filed July 6, 1966, US. Patent No. 3,330,754, which application is a continuation-inpart of application Ser. No. 249,906, filed Jan. 7, 1963, now abandoned; and this application is further copending with application Ser. No. 622,543, filed Mar. 13, 1967, now US. Patent No. 3,340,166,

This invention relates in general to electrochemical machining, and particularly to methods for successfully performing electromechanical trepanning operations. Electrochemical machining of metalloids, sometimes called electrolytic machining, is coming into extensive use because of its ability: to machine any conductive metalloid; to machine metalloids that are not readily machinable by ordinary methods or conventional cutting tools, while still obtaining substantially high surface finish free from burrs; to produce articles free of residual stresses and metallurgical charges; and to machine threedimensional shapes with a single-axis movement.

It is now well known that electrochemical machining consists in advancing an electrode tool toward and into a workpiece while electrolyte is supplied under pressure to the interface between the working face of the electrode tool and the workpiece. A direct current source of low potential but high amperage capacity is connected to the electrode and the workpiece in a sense to make the electrode a cathode and the workpiece an anode. The electrolyte action thus produced rapidly removes material from the anodic workpiece in front of the advancing electrode tool.

Among the major utilizations of electrochemical machining are trepanning operations, that is, the sinking of a cylindrical or irregular shaped cavity by means of a hollow thin-walled electrode in such a way that a core or slug of workpiece material is severed when the hollow tool traverses all the way through the workpiece. This core or slug of metalloid may or may not be the finished article.

The possibility of a damaging short circuit between the cathodic tool and the anodic workpiece exists in all electrochemical operations, 'but especially in electrochemical trepanning operations. A short circuit can occur when a hollow electrode breaks partially through the remote side of a workpiece, permitting the electrolyte to flow suddenly through the workpiece and creating an electrolyte shortage or starvation at the gap between the electrode tool face and the remaining metal in the cavity. Consequently, the electrode tool advances at a faster rate than the metal can be eroded away from the workpiece, causing a short circuit when contact is made between the electrode tool face and the workpiece. Also a short circuit can occur when the electrode breaks partially through the remote side of a workpiece, allowing the partly severed slug or core to be cocked against an interior surface of the hollow electrode resulting in a short circuit at that point. These problems are solved by the present invention by the means hereinafter described.

An object of the invention, therefore, is to provide method and apparatus to prevent short circuits in electrochemical trepanning operations.

Another object of the invention is to provide for more eflicient metal removal as a trepanning electrode tool emerges through a hole in a workpiece.

A further object of the invention is to provide methods and apparatus for preventing a slug obtained by electrochemical trepanning of a workpiece from becoming dislodged and thereby interfering with the machining process and causing a short circuit.

Various other objects and advantages will appear from the following description of several embodiments of the invention, and the novel features will be particularly pointed out hereinafter in connection with the appended claims.

Although the invention is disclosed as it pertains to electrochemical machining, it will be obvious to those learned in the art that the methods and apparatus herein described can be easily adapted to solve similar problems in trepanning operations 'by means of electrical discharge machining, sometimes called spark machining.

In the drawings, wherein like numerals refer to like or equivalent elements:

FIGURE 1 is a front perspective view of an electrochemical machining apparatus;

FIGURE 2 is a structural embodiment of the present invention;

FIGURE 2a is a magnified view of a section of FIG- URE 2 showing the relationship of the tool and the workpiece;

FIGURE 3 and FIGURE 4 shows the relationship between the tool and the workpiece;

FIGURE 4a shows a magnified view of the section of FIGURE 4 showing the relationship of the tool and the workpiece;

FIGURE 5 shows a modification of the slug catcher of FIGURES 2-4.

FIGURE 6 is a schematic representation of a portion of the control circuitry for the structure illustrated in FIG. 1.

FIGURE 1 shows a perspective view of an illustrative embodiment which comprises a hollow base, generally indicated by the numeral 10, on which is mounted a column generally indicated by the numeral 11. The numeral 9 generally indicates a head or ram assembly and consists of an electrode tool 12 connected to the ram assembly by a flange collar 13, as shown in the illustrative embodiment. The tool member 12 extends downwardly into operative engagement with the workpiece 14 held in the workpiece fixture 17 that is disposed in a transparent fixture enclosure 15.

As shown in FIG. 1, the machine column 11 includes the lower spaced apart hollow legs or supports 101 and 102 which form compartments for housing a part of the operating structure of the machine. The numeral 103 indicates the upper end of the column 11 which is integral with the legs 101 and 102 and which encloses the upper end of the area between legs 101 and 102 to form a passageway 104 in which is seated the fixture enclosure 15. The upper end of the base 10 encloses the lower end of the passageway 104. It will be seen that this structure permits the machine to be set up for production line operation whereby workpieces may be moved into and out of the work-piece fixture by suitable Work transfer means. As shown, the legs 101 and 102 are secured to the base 10 by any suitable means as by the screws 25.

The upper end of the column 11 is provided with the compartment in which is mounted the head assembly. The compartment is enclosed on the front side thereof by the hingedly mounted door 27 The fixture enclosure is provided with a bottom plastic wall 111 which is seated on the top Wall portion of the base 10. The enclosure 15 includes the side alls 113 and 115 which are connected to a rear wall not shown, the top wall 117 and the bottom wall 111 by any suitable means, as by a suitable adhesive. The front end of the enclosure 15 is provided with the integral peripheral flange 118 around an excess opening adapted to be closed by the sliding door 119. The door 119 is provided with a knob 122 for manually sliding the door to the left as viewed in FIG. 1 through the opened position. The door 119 is adapted to be slidably mounted on tracks which extend along the left side wall 113 of the enclosure 15. The enclosure 15 is preferably made from plastic to permit inspection of the workpiece and tool during the operation.

The workpiece fixture 17 is mounted on the pedestal 123 which is secured to the surface portion 105 of the base 10. The fixture 17 is supported on the pedestal 123 to clamp the workpiece against the pins or abutting means 136. The illustrative workpiece fixture is adapted to hold any workpiece in a rigid position while a bore is formed therethrough. It will be understood that the form of the fixture will be dictated by the workpiece which is to be machined. A hose 125 is provided for conduction of reduced pressure means, the purpose of which is to be explained hereinafter. A second hose 126 is provided for conducting electrolyte to the tool 12 through the passage 16 shown in FIG. 2.

The drive unit 129 is supported on the rear side of the column portion by any suitable means. The drive unit may include any suitable drive motor and provides the motor power for raising and lowering the tool. The means for raising and lowering the shaft on which the tool is placed is accomplished by any suitable combination gear reduction means not shown but well known in the art.

The tool is provided with connections to the negative terminal of a suitable DC. power supply, not shown. The DC. current circuit is completed from the positive terminal of the power supply to the workpiece by means of a cable connection 131. It will be seen that the tool is negative and the workpiece along with its fixture is positive. The DC. current is passed through to the workpiece 14 for purposes of machining.

Panel 133 is provided with proper switches and buttons to provide control of the machining operations. Panel 135 is provided with regulating valves for controlling the flow of electrolyte.

Referring now to the drawings, and more particularly to FIGURES 2, 3 and 4, thereof, in the course of a typical trepanning operation by electrochemical process a hollow electrode tool 12 electrically connected to the negative terminal of direct current source by appropriate means (not shown) is advanced slowly into a workpiece 14, connected to the positive terminal of the current source by appropriate conductors (not shown) while electrolyte is forced under high pressure through a passageway 16 in the hollow electrode tool. The electrolyte is thus caused to flow across the interface between the advancing working face 18 of the electrode tool and the receding corresponding surface of the workpiece being eroded away by the electrochemical process.

The electrode tool is preferably coated on its outside surface with an adhering film 19 of a material which is a good electrical insulator to prevent electrolysis of the side walls 20 of the cavity being formed in the workpiece, according to a technique which is well known to the art. When it is desired to prevent electrolysis of the slug, the inner surface 21 of the electrode tool may also be coated in a similar manner.

When the electrode tool 12 has penetrated the workpiece to the position illustrated in FIGURE 4, a slug or Cit core 22 is caused to be severed from the workpiece. In most instances, the slug is not separated from the workpiece all at once, and some portions of the bottom of the workpiece cavity are eroded away first, affording an escape passage for the electrolyte and causing a drop of electrolyte pressure and electrolyte starvation at the interface. Due to this electrolyte starvation at the interface, the workpiece cavity is not eroded at as fast a rate as the electrode tool is advancing and a short circuit occurs when the two make contact.

To prevent this from occuring, a back-up member 24 is disposed under the workpiece 14, as shown in the drawing. The back-up member includes a core of slug catcher 80 made of dielectric substance, such as, glass, nylon, plastic or other non-conductive substance. Disposed on the dielectric core or slug catcher 80 and adjacent to the bottom edge of the workpiece, is a recess 28'. The clearance recess 28', is integral with the back-up member 24, the shape of the recess 28' corresponding to the shape of the electrode tool working face 18. The clearance recess 28' forms a support for the underface 36 of the slug 22 when the slug falls away from the workpiece 14.

The recess 28 may be machined slightly larger than the size of the slug 22. That is, the dimensions of the opening in the workpiece is called the print size of the part. The electrode tool is made minus print size and varies from .006 to .012 per side of electrode tool. Therefore, when the part is machined it will cut to print size. The core or slug catcher 80 is made slightly oversize with respect to the width of the slug 22 as shown in FIG. 2a. The reason for the use of a dielectric slug catcher is evident from the views of FIGURES 2, 3 and 4. As the edge 82, which can be made dimensionally different than the edge 83 by a thousandth of an inch or more, electrolytically erodes away the remaining portion of the slug 22, the edge of slug 22 drops into the recess 28', as shown in FIGURE 3. Ordinarily, at this time, any slight misalignment is likely to cause a short circuit. However, since the slug catcher is made of a dielectric substance, no short circuit will occur. However, it is apparent that the recess 28 cannot be too deep or the edge 75 of the slug 22 will drop too far down into the recess causing a short circuit at the gap 85 between the inside edge 86 of the tool 12 and the surface 87 of the slug 22, as shown in FIGURE 3, In other words the working face of the electrode tool must slant from its outer edge to its inner edge at an angle of five to ten degrees (5-10). This will allow the slug to retain its maximum diameter and still provide a maximum clearance at the gap 85 when one edge of the slug is machined away and resting on the slug catcher 80, as shown in FIGURE 3.

FIGURE 4 shows the position of the slug 22 when resting within the recess 28' of the dielectric slug catcher 80. A second recess 81 is provided in the slug catcher 80 to maintain the slug 22 in its break-away position by virtue of well known laws of physics as explained hereinafter. The vent hole or orifice 90 is exited to the atmosphere or other subatmospheric pressure means. Consequently the force of electrolyte fiovving through the passageway 16 of electrode tool 12 being greater on top of slug 22 by means of a larger pressure force impinges upon the slug 22 holding it down in the recess 28'. A small amount of electrolyte that leaks or escapes under the slug will be vented to atmosphere or other subatmospheric means however, the greater pressure force of electrolyte holds the slug down in the recess 28'. In other words, the exit flow of electrolyte through orifice 90 is less then the flow of electrolytethrough the passageway of the electrode tool, thereby the force of the electrolyte holds the slug down in the recess 28'.

As shown in FIGURE 4a, the magnified view of the recess 28' and the bottom edge surface of the workpiece shows that in providing for the recess to be slightly larger than the print size of the hole in the workpiece results in the edge to be deburred.

A further modification, as shown in FIGURE 5, is to provide for the recess 28' of slug catcher 80 to be the same size as the electrode tool. That is, the recess will be made minus print size. However, slug catcher 80 is rounded at the edge adjacent the workpiece such as shown at 95 in FIGURE 5. The rounded edge undercuts the edge of the workpiece 14 and therefore allows the edge 97 of the workpiece 14 to be deburred. However, it is well understood that there exists many other variations and modifications that can effect the same results hereinabove described.

Controlled circuitry for the machine shown in FIG- URE 1 is illustrated in FIGURE 3. The power supply is provided through a 440 volt, 3 phase, 60 cycle line and goes through an ordinary circuit breaker and provides an input to the rectifier, another input to the electrolyte pump motor and a third input to the feed motor. The input to the electrolyte pump motor is protected by fuses SFU, 6FU and 7FU. The electrolyte pump motor is operative through contacts 1M only when the coil 1M is energized. The feed motor is similarily protected by means of fuses 2FU, 3FU and 4FU and operative only when contact 2MF or 2MR are closed, in a manner as will be hereinafter disclosed. The rectifier is operative when coil SCR is energized.

Assuming that the operational cycle is now initiated with the circuit breaker engaged to thus provide power to the transformer IT and thereby provide a conventional flow of electrical power to conductors 201 and 202. A fuse 1FU protects the lines 201 and 202 from excessive surges of electrical power.

The operational cycle is initiated with the tool 12 fully raised or in the uppermost position. Pressing the MASTER START button provides for flow of electrical power into line 203 to energize coil CRM. Energizing coil CRM closes normally-open contacts CRM between line 203 and 205. Electrical power transmitted through transformer 1T flows through line 201 through the MASTER STOP button, through the now closed contact CRM to line 205 and back through line 204 and 203 to maintain or hold the coil CRM energized. With the flow of power going through the MASTER STOP button and now closed contact CRM, line 220 is electrically conductive. With the ELECTROLYTE switch placed in the ON position, electrical power from line 220 fiows in line 209 and energizes coil 1M. Energizing coil 1M closes contacts 1M of the ELECTROLYTE PUMP MOTOR shown to the right of FIG. 3. Closing of contacts 1M causes electrical power to energize the pump motor for flow of electrolyte to the tool 12.

The operating mode of this machine will be first described in the AUTO or automatic cycle. The flow of electrical power in line 205 goes through the CYCLE switch and energizes coil CRA. Energizing the coil CRA closes the normally-open contacts CRA in line 208. With the tool in the retracted position, which would be considered the start cycle position, the limit switch 1LS is closed thus electrical power flows in line 206 to energize coil 1CR. Energization of coil ICR opens the normallyclosed contacts ICR in line 207 thereby preventing the flow of electrical power to energize coil SCR unless limit switch 3LS is closed.

The operational cycle is initiated when the START CYCLE button on line 214 is pushed, thereby providing a flow of electrical power through the now closed contacts CRA, the closed contacts of STOP CYCLE button, the now closed contacts of the START CYCLE button, the now closed contacts of lCR, the now closed contacts of 1M, and finally through the normally-closed contacts of 3CR to energize coil 4CR.

Energization of coil 4CR on line 214 closes contacts 4CR on line 215 to maintain energization of coil 4CR. To deenergize the coil 4CR, the STOP CYCLE button has to be pressed dropping out the coil 4CR and stopping further operation of the machine. Closing of the contacts 4CR in lines 217 and 218 when the START CYCLE button is depressed provides for flow of electrical power to line 216 to energize coil 5CR .Energization of coil 5CR closes contacts SCR shown to the right of FIG. 3. Closing of the contacts SCR causes electrical power to fiow to the rectifier. Simultaneously, the energization of coil 4CR closes contacts 4CR on line 213 thereby causing electrical power to flow in line 212 through the closed contacts of the JOG UP button, through the normally-closed contacts 2MR to energize coil 2MF. Energizing coil 2MF closes the contacts 2MF of the FEED MOTOR and causes the motor to rotate forward to move the tool 12 shown in FIG. 2 downward. As the tool starts down, the limit switch lLS on line 206 opens thereby tie-energizing the coil 1CR. De-energizing of coil 1CR closes the contacts lCR in line 207. When the tool reaches its lowermost position, limit switch 3L8 on line 208 closes thereby energizing coil 3CR. Energization of coil 3CR closes contacts 3CR in line 211. Simultaneously, the closed contacts 30R on line 214 are opened thereby de-energizing coil 4CR. De-energization of coil 4CR opens the contacts 4CR on line 213 thereby preventing energization of coil 2MP. De-energization of coil 2MF ceases the rotation of the FEED MOTOR, and simultaneously closes the contacts 2MP on line 210. Electrical power now flows from line 220, through line 211 by means of closed contacts CRA, normally closed contacts 1CR, and now closed contacts of SCR, through line 210 by means of now closed contacts 2MF to energize coil 2MR. Energization of coil 2MR closes contacts 2MR of FEED MOTOR to thereby immediately reverse the rotation of the motor and cause the tool to retract. Closing of the limit switch 3LS provides for energization of the coil 3CR in line 208. Energization of the coil 3CR in line 208 closes the contacts in line 207 maintaining energization of coil 3CR, even though limit switch 3LS is opened when the tool begins to retract. This maintains the rotation of the feed motor in the reverse or upward direction until the tool reaches is uppermost position. As soon as the tool reaches its uppermost limit the contacts of limit switch lLS are closed thereby energizing the coil 1CR of line 206, Energization of coil 1CR opens the contacts 1CR on line 207 and prevents further electrical flow to energize coil 3CR and 3CR drops out or de-energizes. De-energization of coil 3CR opens the contacts 3CR on line 211 and stops further energization of 2MR which ceases rotation of the feed motor. The tool remains in its uppermost position or fully retracted position until the START CYCLE button is depressed on line 214 thereby energizing coil 4CR. Energizing coil 4CR causes the forward rotation of the feed motor in the manner described above.

When it is desired to operate the machine in a manual mode of operation, the switch in line 205 is turned to HAND and thereafter all operations are not automatic but are manual. The JOG DOWN on line 212 and the JOG UP on line 210 will depend on the operator making all of the necessary operations to cause the machine to go down or up. The rectifier is put in operation by pressing the RECT. ON button in line 216 which causes electrical power to flow through line 216 to energize coil SCR. Energizing coil SCR closes contact SCR in line 219. Since the contacts CRA in line 219 are normally closed, closing of contacts 5CR provides a by-pass to maintain coil 5CR in the energized position at all times, unless the RECT. OFF button is pushed thereby preventing electrical power to flow in line 216.

It is seen from the methods and apparatus heretofore described, that the problem of short-circuits in electrochemical trepanning operations has been solved by the use, when necessary, of a recess and pressurized electrolyte supply in the back-up member, and by the use of means to hold the slug in its original position after the electrode breaks through the remote side of the workpiece.

It will be understood that the direction and orientations, such as up or down, top or bottom, mentioned in the above description refer only to the attached drawings and will not necessarily be the same in actual applications of the invention.

It will be also understood that various changes in the details, materials, steps, and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

What is claimed is:

1. In the process of electrolytically trepanning an electrochemically erodible workpiece by means of passing current between a hollow electrode tool and said workpiece, said electrode tool having a conductive working face and at least one electrolyte passage therethrough for supplying electrolyte under pressure to said working face, the improvement in the method comprising the steps of:

(a) moving the electrode tool relative to the workpiece in such a way as to define a narrow gap between said electrode tool working face and said workpiece wherein a slug of non-eroded workpiece material is adapted to be served from said workpiece;

(b) flowing an electrolyte fluid under pressure through said hollow electrode tool;

(c) providing a back-up member for said workpiece;

said back-up member having a recessed area substantially conforming to the shape of said electrode tool working face, and wherein said recess is adapted to be in contact with at least a portion of said slug;

((1) reducing the pressure in said recess below the presence of said flowing electrolyte for holding said slug when said electrode tool has penetrated through said workpiece and emerges therefrom into the recessed area of said back-up member;

(e) said recessed area of said back-up member having a dielectric surface whereby electrode shorting is prevented when said slug is in said recessed area.

2. In the process of electrochemical trepanning as defined in claim 1, wherein said reduced pressure is effected by providing said recessed area with an orifice in fluid communication with a source of reduced pressure to immobilize and hold said slug when said electrode tool working face has penetrated all the way through said workpiece and emerges into said recessed area of said back-up member.

3. The method of claim 3 wherein said orifice is connected to the atmosphere.

4. In, an electrochemical trepanning apparatus including means for holding a workpiece, an electrode tool for trepanning said workpiece, said electrode tool having a working face at one end thereof, means for advancing said electrode tool relative to the workpiece and for maintaining a gap therebetween, means for rapidly circulating an electrolyte through said gap at a high pressure, and a source of electric current electrically connected to the workpiece and said electrode tool to make said workpiece predominantly anodic and said tool predominantly cathodic, the improvement wherein said tool has an axial bore terminating at said face to provide at least one electrolyte passage therethrough for supplying electrolyte under pressure to said gap; said means for holding the workpiece includes a back-up member for supporting said workpiece and having a dielectric-surfaced recessed area conforming to the shape of said electrode tool working face, and positioned to receive at least a portion of said workpiece cut away by said electrode tool; and said back-up member having an orifice to provide fluid communication between said recessed area and a source of reduced pressure to immobilize said cut away portion of the workpiece when said electrode tool working face has penetrated through said workpiece .and emerges into said recessed area of said back-up member.

5. The apparatus of claim 4 wherein the working face of said electrode tool slants axially and radially inwardly at an angle in the range of from about 5 to about 10 from said plane.

6. The apparatus as defined in claim 4 wherein said orifice is communicating with atmosphere.

7. The apparatus as defined in claim 4 wherein said orifice is communicating with suction inlet of a pump circulating and placing the electrolyte under pressure.

8. In an electrochemical trepanning apparatus, as defined in claim 4 the improvement further comprising:

(a) said recessed area of said back-up member having an insert of dielectric material with a recessed area thereon substantially conforming to the shape of said electrode tool working face; and

(b) an orifice connecting said recessed area to the atmosphere; whereby said slug is adapted to be secured in said recessed area by virtue of the differential pressure existing between the inlet flow of the electrolyte fluid through said electrode tool and the exit flow through said orifice.

References Cited UNITED STATES PATENTS 3,058,895 10/1962 Williams 204143 ROBERT K. MIHALEK, Primary Examiner. 

